1. Field of the Invention
The systems and methods of this invention relate to electrical stimulation of the cochlea of the ear and to cochlear nerves and to regions proximal to cochlear nerves of the ear as a treatment for hearing loss. Specifically, the present invention relates to methods and apparatus for applying such stimulation to selected regions of the cochlea without the use of leads of conventional cochlear implant systems.
2. Description of the Background Art
Electrical stimulation in the cochlea of the ear for the purpose of treating patients with hearing loss has been known and actively practiced for several decades. Application of an electrical field between electrodes in the cochlea stimulates cochlear nerve tissues and is known to effectively modify signal pathways to the brain to emulate the sensation of hearing sounds. These applications currently use several components including externally applied parts and implanted parts, collectively referred to as a cochlear implant system (CIS). A cochlear implant system consists of a microphone, which picks up sound from the environment; a sound-speech processor, which selects and arranges sounds picked up by the microphone; a transceiver-stimulator, which receives signals from the sound-speech processor and converts them into electric impulses; and electrodes, which collect the impulses from the transceiver-stimulator and applies them to the cochlea. As the cochlea is stimulated, signals are sent to the brain and interpreted by the brain as sound.
A CIS device does not restore or create normal hearing, nor does it amplify sound like a hearing aid. CIS provides a train of stimulation pulses that are correlated with sound and provides this interpreted pattern of impulses to the brain. The brain is capable of associating these substituted impulses as sound which enables the patient/brain to reform environmental sound recognition and speech recognition. Depending on the individual patient, cochlear stimulation can effectively activate signal pathways along the cochlear nerve, to the brain, and the brain associates these artificially induced impulses with sounds. For example, speech recognition can be accomplished in profoundly deaf patients who learn to associate these stimuli with sound, particularly in combination with reading lips. Treatment regimens and targeted cochlear nerve locations are known in related art through use of current, common stimulation devices and methods. Commonly implanted CIS devices for cochlear nerve stimulation are made by such companies as Med El Medical Electronics, Advanced Bionics, Cochlear Inc. and others.
As illustrated in FIG. 1, the hearing system is an anatomical structure that begins at the ear canal. Sound travels through the canal to the ear drum which vibrates and sets in motion bones in the inner ear. This motion causes the fluid in the cochlea to move small hair cells. The hair cells transduce this movement into electrical impulses in the cochlear nerve which sends the impulses to the brain, which then interprets the impulses as sound.
CIS is a well known medical treatment used primarily to restore speech recognition in the patients with conditions that prevent the hair cells in the cochlea from activating, particularly in the profoundly deaf. Use of the CIS components (microphone, sound-speech processor, transceiver-stimulator, and electrodes) for a conventional CIS device is illustrated in FIG. 2a. The Microphone is typically worn behind the ear and configured for wear to hook over the top of the ear or alternatively can be worn on the clothing or placed in a pocket. There is a direct connection from the Microphone, via a wire, to the Sound-speech processor. Alternative embodiments sometimes include the Microphone and the Sound-speech processor in the same device. The Sound-speech processor interprets the sound waves it receives and converts the frequency of the sound waves into trains of pulses with varying pulse durations. The series of pulses is then sent to the Transceiver-stimulator to be converted into electrical signals to be sent between electrodes that are positioned in the cochlea. This series of pulses is communicated from the Sound-speech processor either by direct wired connection to the Transceiver-stimulator or by radiofrequency communication between the two components. The Transceiver-stimulator is implanted subcutaneously between the patient's skin and skull and the Sound-speech processor may be mounted externally on the skull proximate to the Transceiver-stimulator. The Electrodes are connected to the Transceiver-stimulator via a lead that is tunneled from the cochlea to the Transceiver-stimulator. Electrodes are dispersed along the distal end of the lead and positioned throughout the cochlea so that a variety of locations in the cochlea can be stimulated independently. Prior art describes effective processes and algorithms to convert sound into impulse trains and to send those trains to electrodes in selected cochlea regions to stimulate the cochlear nerves.
In CIS systems, electrical energy is delivered through lead wires to the electrodes. As shown in FIG. 2b, CIS implanted electrodes are positioned throughout the spiral structure of the cochlea in order to stimulate different regions in the cochlear nerve. CIS uses the implanted electrodes to deliver a variety of stimulation modalities along the cochlea and thus along the cochlear nerve with the electric pulse waveform defined by a plurality of variables, including but not limited to: pulse width or pulse frequency (Hz).
As described above, CIS devices are battery-powered electronic devices connected via insulated metal lead(s) to electrodes which are placed in the cochlea around or in close proximity to the cochlear nerve or cochlear nerve bundle. The implanted electrodes for CIS are positioned on leads that are placed percutaneously, through needle punctures or through direct surgical access to position the electrodes along the spiral shaped cochlea. A typical application may utilize 16 electrodes (for example, selected and used as 8 pairs of electrodes) positioned in regions that are targeted for electrical stimulation. The implanted leads are then subcutaneously tunneled to the Transceiver-stimulator (also referred to as a controller) that is implanted in a subcutaneous pocket between the skin and the skull. The use of these lead wires is associated with significant problems such as complications due to infection, lead failure, lead migration, and electrode/lead dislodgement. Application of electrodes to the cochlea can be difficult because of the need to locate electrodes for effective therapy. Additionally, the implanted Transceiver-stimulator must be in communication with the external Sound-speech processor. This requires that the implanted Transceiver-stimulator have a percutaneous connection to the Sound-speech processor or that an RF or magnetic coupling be maintained. A percutaneous connection is often a source for infection and wound control.
Other prior art in many stimulation applications has attempted to deal with the complications and limitations imposed by the use of electrical leads. For example, self-contained implantable microstimulators and remotely powered microstimulators have been described; however each approach suffers from some significant limitation. A self-contained microstimulator must incorporate a battery or some other power supply; this imposes constraints on size, device lifetime, available stimulation energy, or all three. Constant communication from the Speech Processor would be required with the microstimulator imposing further constraints on maintaining a constant communication between the two devices. Due to high use or high energy requirements of the therapeutic stimulation some CIS devices contain rechargeable batteries or are powered remotely with the RF coupling to the controller.
For non-percutaneous connection solutions, between the Sound-speech processor and the Transceiver-stimulator, CIS devices have previously utilized either radiofrequency (RF) or electromagnetic transformer power transmission. RF energy transmission, unless the transmitting and receiving antennae are placed in close proximity, suffers from inefficiency and limited safe power transfer capabilities, limiting its usefulness in applications where recharging or stimulation must be accomplished at any significant depth (>1-2 cm) within the body. Electromagnetic coupling can more efficiently transfer electrical power, and can safely transfer higher levels of power (devices with capacity in excess of 20 Watts have been produced) but again relies on close proximity between transmitting and receiving coils.
The methods and apparatus of the current invention utilize vibrational energy, particularly at ultrasonic frequencies, to overcome many of the limitations of currently known solutions for cochlea stimulation, by achieving a cochlea stimulation capability without direct connection to the Sound-speech processor or without the use of leads connected to a controller.
The following patents, all of which are incorporated in this disclosure in their entirety, describe various aspects of using electrical stimulation for achieving various beneficial effects by cochlear implant systems. U.S. Pat. No. 3,751,605 titled “Method for Inducing Hearing” by Michelson describes methods for inducing the sensation of intelligible hearing by direct electrical excitation of the auditory nerve endings distributed along the basilar membrane within the cochlea. U.S. Pat. No. 4,400,590 titled “Apparatus for multichannel cochlear implant hearing aid system” by Michelson describes an intra-cochlear electrode array for electrically stimulating predetermined locations of the auditory nerve within the cochlea of the ear. U.S. Pat. No. 4,819,647 titled “Intracochlear electrode array” by Byers et al. also describes an intra-cochlear electrode array for electrically stimulating the cochlea of the ear. U.S. Pat. No. 6,671,559 titled “Transcanal, transtympanic cochlear implant system for the rehabilitation of deafness and tinnitus” by Goldsmith et al. describes an implantable application for cochlea stimulation using a system that couples communication and energy via RF or inductive coupling. U.S. Pat. No. 6,889,094 titled “Electrode array for hybrid cochlear stimulator” by Kuzma describes an implantable cochlear electrode array. U.S. Pat. No. 5,405,367 titled “Structure and Method of Manufacture of an Implantable Microstimulator” by Schulman et al. describes an implantable microstimulator used generally for stimulation of tissue. U.S. Pat. No. 6,037,704 titled “Ultrasonic Power Communication System” by Welle describes the use of ultrasound energy transfer from a transmitter to a receiver for purposes of powering a sensor or actuator without being connected by a lead/wire. U.S. Pat. No. 6,366,816 titled “Electronic Stimulation Equipment with Wireless Satellite Units” by Marchesi describes a tissue stimulation system based on a wireless radio transmission requiring the charging of a battery at the receiver and separate command signals used to control the delivery of stimulation. German patent application DE4330680A1 titled “Device for Electrical Stimulation of Cells within a Living Human or Animal” by Zwicker describes a general approach to power transfer using acoustic energy for tissue stimulation.